On the structure and oxygen transmission rate of biodegradable cellulose nanobarriers
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NANO EXPRESS
Open Access
On the structure and oxygen transmission rate of biodegradable cellulose nanobarriers Gary Chinga-Carrasco* and Kristin Syverud
Abstract Cellulose nanofibrils have been proposed for novel barrier concepts, based on their capability to form smooth, strong and transparent films, with high oxygen barrier properties. A series of cellulose-based films were manufactured and tested with respect to their oxygen transmission rate (OTR) capabilities. The obtained OTR levels were considerably better than the levels recommended for packaging applications. Part of the nanofibrillated material applied in this study was produced with 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO) mediated oxidation as pretreatment. Films made of TEMPO-pretreated samples yielded lower OTR values. The minimum obtained OTR value was 3.0 mL m-2 day-1 atm-1 with a corresponding oxygen permeability of 0.04 mL mm m-2 day-1 atm-1, tested at 50% relative humidity. The good barrier properties are due to the compact and dense structure of the films, as revealed by field-emission scanning electron microscopy. A relationship between OTR and the structure of the corresponding nanofibril-based films was confirmed. Keywords: Nanoparticles, Polymers, Porous materials, Cellulose, Films
Background Cellulose nanofibrils are nano-components of a cellulosic material produced through a fibrillation process [1]. Several applications have been envisaged for cellulose nanofibrils due to their particular rheological, optical and strength properties [2-6]. The materials have also been proposed for packaging applications, based on their capability to form smooth, strong and transparent films, with high oxygen barrier properties [5,7-10]. However, films made of cellulose nanofibrils are hydrophilic, having low moisture barrier properties. Surface modification has thus been proposed for reducing water wettability [7,10,11], which may be necessary in food packaging applications. The density of nanofibril-based films is an important property to quantify, considering their potential application as barriers in packaging. The density gives an indication of the consolidation of the films during production. The more consolidated a given film is, the larger the density. Yang et al. [12] reported a relationship between the oxygen transmission rate (OTR) and the density of regenerated cellulose films. The intrinsic * Correspondence: [email protected] Paper and Fibre Research Institute (PFI), Høgskoleringen 6b, Trondheim, 7491, Norway
thickness of relatively thin films is an essential measure for estimating the density of the material. The thickness of cellulose films can be measured with electron microscopy techniques, as reported recently [13]. In addition, the crystallinity degree of a given cellulose material has been reported to affect the OTR [5,8], i.e. increasing the crystallinity degree reduces the oxygen permeability. The purpose of this study is to shed light on the structure of nanofibril-based films and on how this complex structure lim
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